Generally, a nanogap can be applied to an electrode, so that the nanogap can be used to research the electrical characteristics of a nanoscale structure or can be utilized as a sensor for sensing an extremely small amount of chemical materials or biological materials. Particularly, the nanogap is necessarily used to measure variation in electrical characteristics at the molecular level.
Recently, a method of forming a gap at a predetermined location in a metal wire using an electromigration phenomenon (Appl. Phys. Lett 75, 301), a method of fabricating a nanogap using electron beam lithography (Appl. Phys. Lett 80, 865), a method of forming a relatively large gap and then decreasing the size of the gap using an electrochemical deposition method (Appl. Phys. Lett 86, 123105), a method of fabricating a nanogap using a shadow mask (U.S. Pat. No. 6,897,009), etc. have been proposed as methods of fabricating a nanogap.
However, in the method of forming a nanogap at a predetermined location in a metal wire using a electromigration phenomenon, in which the metal wire having a line width of several tens to several hundreds of nanometers is prepared, a current is caused to flow through the metal wire so that atoms of the metal wire gradually move and thus a predetermined portion of the metal wire is disconnected, thereby forming the nanogap having a width of several nanometers, it is difficult to accurately control the position and size of the nanogap.
Further, in the method of fabricating a nanogap using electron beam lithography, which is a direct patterning method using the electron beam, a precise nanogap can be obtained, but it is difficult to fabricate the nanogap in large quantities.
Further, Korean Patent Application No. 10-2004-0082418 discloses a method of forming a nanogap electrode by placing a spacer on one side of a first electrode, forming a second electrode, and then removing the spacer. However, the method has disadvantages in that the processes therefor are complex, it is difficult to adjust the width of the nanogap, and it is impossible to form a plurality of nanogap electrodes simultaneously.
Further, in the method of forming a nanogap using an electrochemical deposition method, in which metal electrodes, spaced apart from each other by relatively large gaps, are formed on a predetermined substrate, electric terminals are connected to the metal electrode patterns, the entire substrate is dipped into an electrolytic solution, and then voltage is applied thereto, so that an electrode layer is deposited on the surface of the metal electrode pattern, with the result that the electrode layer becomes thick thus gradually decreasing the width of the gap, thereby forming the nanogap therebetween, the processes therein are complex, and it is difficult to adjust the size of the nanogap.
Further, in the method of fabricating a nanogap using a shadow mask, in which a nanostructure such as a nanotube is placed, and then a metal material is deposited thereon, thereby forming a nanogap having the same size as the nanostructure, the size of the formed nanogap depends on that of the nanostructure, and it is difficult to form the nanogap at a desired place.
As such, in consideration of attempts to produce a nanogap using conventional semiconductor process technologies, it has been difficult to economically and efficiently produce the nanogap in large quantities, and thus it has been limited in use to the direct evaluation and analysis of the electrical characteristics of nanoscale materials such as single molecules, nanoparticles, protein and DNA. However, the nanoscale materials have been able to be handled using electrodes having nanoscale gaps due to continuous advancement in semiconductor process technologies. If these technologies are used, it is possible to measure physical or electrical characteristics, such as conductivity etc. of a single molecule or nanoparticles. Moreover, nanoscale electronic devices, such as a nanoscale rectifier and a nanoscale transistor, have been developed by controlling the current flowing through a molecule. Further, research on biotechnology, such as a biological device used to observe the variation in electrical characteristics of protein, DNA and the like when they are placed between the electrodes having nanoscale gaps therebetween and medicine is administered to them, have rapidly advanced. The important technology in the development of molecular electronic devices, biological devices and the like is a technology of forming metal nanogaps having nanoscale gaps, in which nanoscale materials can be secured at desired places.
Accordingly, a technical problem still remaining in the related art is that there is no method of conveniently, economically and efficiently fabricating a nanogap.